[clang] [Clang] Add GCC's __builtin_stack_address() to Clang. (PR #121332)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for this!

Please also be sure to add a release note to `clang/docs/ReleaseNotes.rst` as well as document the extension in `clang/docs/LanguageExtensions.rst` so users know about the functionality.

Should we be supporting `STACK_ADDRESS_OFFSET` similar to what GCC does?

https://github.com/llvm/llvm-project/pull/121332